Such network systems for television are commonly known as "PAY-TV" networks. In such a system an administering company manages the network. It controls distribution of special receivers to only those users who pay a participation fee for obtaining access rights to the network. The special receiver is of the type which is able to receive and decode the desired programs. A user who stops paying will be excluded from the network by disconnection or by removal of the receiver.
However, there have been problems with dishonesty in such networks. For example, some people have removed a receiver, "reverse engineered" it and finally copied it so as to avoid paying the administering company.
In response to this, so as to avoid or hinder copying of their receivers, the companies have provided their receivers with very unusual components specially developed for very sophisticated methods of coding/decoding broadcast signals. As these sophisticated and expensive receivers are not cheap, a large number of old receivers have still not been replaced. With such a system, despite numerous efforts to control the number of authorized users of such networks, a large number of clandestine users are known to exist already and it is estimated that this number will increase.